Detection and discrimination of amplitude modulation

Abstract

Amplitude-modulated stimuli have been used in psychophysical experiments to address a variety of issues including intensity discrimination, frequency and temporal resolution, and roughness perception. Thresholds for detecting amplitude modulation (AM) and discriminating a change in AM rate or depth are the basis for much of this work. Early work emphasized the role of the peripheral excitation pattern in AM detection. More recent studies have often concentrated on the temporal aspects of modulation coding. With sinusoidal AM, the change in detection threshold as a function of modulation rate is commonly interpreted as a temporal modulation transfer function (TFTF) and has been used to assess temporal resolution. Stimulus parameters that affect the TMTF include carrier spectrum, level, and gating characteristics. The effects of these parameters and implications for AM processing will be reviewed. This current work measures the ability to discriminate a change in either modulator phase or envelope regularity as a function of AM rate. Irregular AM was generated with frequency modulation of a sinusoidal envelope modulator. Results from these experiments will be discussed in terms of auditory processing of modulation as characterized by the TMTF. [Work suported by NIH.]